An improved region growing algorithm for automatic segmentation kidney from abdominal CT image is proposed.Compared to original region growing method,this method automatically selected initial seedpixels and is robust to the order of region growing.Firstly,computing the neighbor similarity factor (NSF) based on local histogram of each pixel and spatial information of local pixels.Then,building the criteria of initial seedpixels,region growth and region growing termination based on NSF.Finally,MICCAI metrics are adopted to measure the segmentation accuracy.Experimental results demonstrated the performance of method.